Casting method using latent heat of chill material



Dec. 5, 1967 R. H AHRENS 3,

CASTING METHOD USING LATENT HEAT OF CHILL MATERIAL Filed Oct. 20, 1965 2 Sheets-Sheet 1 ATTORNE-I$ Dec. 5, 1967 R. H. AHRENS 3,356,128

CASTING METHOD USING LATENT HEAT OF CHILL MATERIAL Filed Oct. 20, 1965 2 Sheets-Sheet 2 F I BY *MIL ATTOIZMEYS from being dislodged from the sand core. All of the commonly used chills above described are wholly dependent for chilling on the value of their mean specific heat and their mass.

United States Patent Ofiice 3,356,128 CASTING METHOD USING LATENT HEAT F CHILL MATERIAL Robert H. Ahrens, Milwaukee, Wis., assignorto Milwaukee Chaplet 8: Mfg. Company, Inc., Milwaukee, Wis.,

a corporation of Wisconsin Filed Oct. 20, 1965, Ser. No. 498,725 4 Claims. (Cl. 164-127) ABSTRACT OF THE DISCLOSURE Chill efficiency in promoting localized hardening of molten metal in a mold is enhanced by incorporating in a unitarily prefabricated chill to be inserted in the mold, a material which undergoes change of state sufficiently below the temperature at which the molten metal congeals to maintain temperature differential but sufficiently close to the congealing point of the molten metal so that the latent heat will be effective, thereby substantially maintaining predetermined temperature differential between the molten metal and the chill until congealing occurs. Change of state may be from solid to liquid or from liquid to gas.

The present application is a continuation-in-part of my application which was filed August 27, 1965, Serial No. 483,089, now abandoned having the same title. This invention relates to a foundry chill method.

It is the object of the invention to withdraw heat from molten metal in a mold to cool such metal rapidly and effectively and prevent shrinkage of the casting away from the core or mold. From an apparatus standpoint, the present invention is primarily intended for use as an external chill which will remain embedded in the mold or core. Normally it will contact a face of the casting, but may sometimes be separated therefrom by sand of the mold.

The chills commonly used industrially may comprise stampings if the amount of heat to be extracted is nominal. For greater heattransfer, they may be cast or forged. When unusual shapes are involved or relatively high mass is required, foundries frequently cast their own chills. Because castings are generally porous, entrained air often acts as an insulating element and prevents the effect of using such chills in successive operations from being uni- .form or'predictable. Forged chills are frequently made in standard configuration, usually being quarter-round in cross sectional shape with anchoring legs to prevent them The present invention contemplates a chill which uses for heat absorption a secondary material, usually a metal,

which changes in state (i.e., changes from solid to liquid I or from liquid to gas) at a temperature below the melting temperature of the metal which is being cast. While the secondary material is usually a metal, it may be an appropriate non-metallic solid or even a liquid. This secondary material is confined by a heat conducting shell made of I material which does not melt in usage, and which, therefore, maintains the secondary material in position after change of state of the secondary material occurs. The use of a secondary material which changes in state during the functioning of the chill, takes advantage of two important thermal characteristics other than mere mass. In the first place, it utilizes the latent heat of change of state of the secondary material. In the second place, assuming that the change of state is a change from solid to liquid, the invention utilizes the fact that the specific heat of a fusible 3,356,128 Patented Dec. 5, 1967 .tion to the metal which is being cast, such material having a melting point or vaporizing point low enough so that change of state occurs at or before the congealing of the metal being cast. Normally, it is contemplated that the molten metal to be cast may be confined at least in part by a heat transfer Wall of material having a melting point sufficiently high so that it will not be destroyed by the molten metal, there being behind such wall, and in heat conductive relation thereto, a secondary body of chill material which changes state at a temperature lower than that at which the metal which is being cast congeals. It is intended that the material of the secondary body be melted or vaporized by heat transferred to it through said wall, both the mass and then the latent heat of change of state of the secondary material, and finally the increase in its specific heat consequent upon its becoming melted (assuming that the change of state is a melting of the secondary material) being utilized to increase and prolong the rate of heat transfer out of the molten metal and thereby to expedite the congealing thereof.

There are advantages in the use of a secondary material as above described in that the chill temperature is maintained at the temperature of change of state of the secondary material for an appreciable period of time so that the differential between the cast metal and the chill remains more effective during such period than is the case when a conventional chill becomes increasingly heated while the casting is congealing. Because the rate of heat transfer is proportionate to the differential temperature, heat is transferred from the casting into the chill at a higher rate and the casting in contact with the chill congeals more rapidly.

Also, if the change of state involves a melting of the secondary material, then, as the secondary material begins 1 to melt, a wet contact is effected between the confinexpensive, takes .less space and provides cleaner, safer and more comfortable conditions for the worker than is possible in the use of conventional chills. Asa consequence, the cost of fabricating bi-metal chills is less than the cost of forged chills.

In the drawings:

FIG. 1 is a view in cross section showing a chill embodying the invention.

FIG. 2 is a view in cross section through a modified embodiment of the invention.

FIG. 3 is a view in side elevation of the device shown in FIG. 2, portions being broken away.

FIG. 4 is a view in cross section through another embodiment of the invention.

FIG. 5 is a perspective view of the chill shown in FIG. 4.

FIG. 6 is a fragmentary detail view in cross section through a mold in which the chill of FIGS. 4 and 5 is incorporated for use.

FIG. 7 is a diagrammatic chart showing the relation of chill and cast metal temperatures in a typical usage of the invention.

The surface 8 of the shell 10 conforms to the desired shape of a wall portion of the casting to be made through the use of the chill. Shell 10 has a melting point sufiiciently high to preserve its integrity in use, usually being as high or higher than that of the metal to be cast. The shell never, in practice, reaches its melting point.

Behind or within the shell 10 is a body of secondary material which changes state to absorb heat with no increase in temperature. It is preferably a solid having a melting point sufiiciently low so that it will become molten when the chill is in use, and preferably coincidentally with the congealing of the metal being cast. Such a body 12 of secondary material desirably may be cast, pressed or sintered within the shell but it may be prefabricated and placed therein. The advantage of casting, pressing or sintering it into the shell is to assure an immediately intimate heat transfer relationship between the shell and the body of secondary material.

As already indicated, the body of secondary material may be a liquid which will vaporize and absorb latent heat during the use of the chill and preferably coincidentally with the congealing of the metal being cast. In case the change of state of the secondary material involves vaporization, the vapor will normally re-condense almost immediately after forming and moving by convection out of the high temperature zone. There is a great temperature differential and heat picked up at the surface of the casting and causing either melting or vaporization is normally given off immediately after change of state as the result of short convection travel of the secondary material.

The secondary material may be entirely sealed within the shell. However, the shell as illustrated in FIG. 1 has neither a back nor ends. When in use, it is embedded in the sand of the mold or core. An anchor 14 is engaged in the sand and holds the chill in place. If the secondary material changes state by fusion at the temperature at which the metal being cast is intended to congeal, the sand of the mold or core cooperates with the shell to confine the secondary material to retain it within the shell when the secondary material is melted as hereinafter described.

In the chill shown in FIGS. 2 and 3, the shell 100 is tubular and optionally closed at both ends to seal the secondary material therein. The anchor or anchors 140 are rods which extend through the shell and the secondary material 120 therein and project at their end portions 16 to be embedded in the sand. Because the secondary material is wholly confined within the shell 100, this shell may be put into the mold or core in any position. It may either be in contact with the metal to be cast, or it may be spaced therefrom by an intervening body of sand, or one end may project out of the body of sand.

In the embodiment shown in FIGS. 4 to 6, the surface 81 of the shell 101 is concave rather than convex and the anchors comprise laterally projecting flanges 141.

As shown in FIG. 6, any chill embodying the invention is intended to be set in the sand 18 of a mold or core 20 with the surface 8 or 81 usually exposed to the molten metal introduced into the mold cavity 22. If the secondary material is a solid which is not fully enclosed, the sand abuts any exposed surfaces of the secondary material 121, thereby holding the secondary material in the shell when the secondary material becomes melted.

When the molten metal to be cast is poured into the mold, the chill will withdraw heat from the molten metal much more rapidly than the heat of the molten metal could otherwise escape through the sand of the mold. Such withdrawal of heat is partly attributable to the change in state of the secondary material and is partly due to convection, since the fluidity of the secondary material enables it to carry the heat to any other cooler surface with in the range of movement.

The heat transfer from the molten metal of the casting to the shell and the body of secondary material therein will be high. The bi-metal chill will absorb heat, in the first instance, strictly upon the basis of its mass and other characteristics such as its specific heat and coefficient of heat transfer. However, the secondary material will shortly reach the temperature at which it changes state. As change of state proceeds, it will absorb heat to supply its latent heat of change of state without any resultant increase in the temperature of the chill as a whole. In consequence, inasmuch as the rate of heat transfer is dependent very materially upon the temperature differential between the chill and the molten metal which is being cast, the maintenance of the temperature of the chill at a static value throughout this critical period will greatly increase the rate of heat transfer and will therefore greatly increase the rate at which the cooling and congealing of the casting is elfected.

FIG. 7 graphically illustrates the functioning of the invention in the making of a ferrous casting. A line of dashes 30 represents the temperature curve of a solid iron chill such as is conventionally used in making such a casting, and the dash line illustrates graphically the resulting temperature changes in the cast metal as it cools when a conventional chill is used.

In contrast, the line of dots at 34 shows the progressive changes of temperature in a chill using a metallic secondary material according to the present invention while the line of dots at 36 shows how much more rapidly the casting is cooled when the bi-metallic chill is used. As shown by the graph, a much longer time is required to solidify the metal in the casting when a solid chill is used than is required to bring about this result when a bi-metal chill is used in accordance with the disclosure hereof. The graph is based on the assumed use of aluminum as the body of secondary material, but it is to be understood that the secondary material, as well as the metal used to make the shell, will vary according to the work. In general, it is desired that the secondary material will be subject to change of state in the approximate range in which it will do the most good in effecting the congealing of the metal which is being cast.

While I have referred in some instances to a bi-metallic chill (FIG. 7 being an example), it will be understood that even if the selected material is a solid the secondary material is not necessarily a metal. It may be a salt or some other material having the desired high mass and appropriate melting point. Thus, while a solid secondary material will normally be metallic, it is desired to emphasize the fact that this is not necessarily the case and generic coverage is intended.

I claim:

1. A method of casting molten metal, which method comprises transfer of heat from the molten metal to effect change of state of a body of secondary material which is subject to change of state at a temperature lower than the congealing temperature of the molten metal but sufficiently close to such temperature so that change of state occurs coincidentally with the congealing of the metal being cast, and thereby using latent heat of the secondary material to absorb a part of the heat of the molten metal and to maintain approximately constant temperature dilferential between the secondary material and the metal being cast throughout a substantial part of the period required for the congealing of the latter, whereby such congealing proceeds more rapidly than elsewhere.

2. A method according to claim 1 in which at least a part of the change of state of the secondary material involves the vaporization thereof.

3. A method according to claim 1 in which at least a part of the change of state of the secondary material involves melting thereof, the secondary material being iniy a and.

4. A method of casting molten metal in a mold, which method comprises the steps of prefabricating a shell, incorporating at least partially in the shell a body of secondary material subject to change of state near the congealing temperature of the metal to be cast in said mold, setting said shell and body into a mold with the shell exposed and the body of secondary material confined, and thereupon pouring into said mold into contact With the shell the metal which is to be cast, and transferring heat from said last mentioned metal into the shell and through the shell into the body of secondary material to effect the change of state of the secondary material and the absorption thereby of heat from the cast metal to supply the latent heat of change of state of the secondary material, whereby to maintain temperature differential between the chill and the molten metal until the latter con- 1,891,792 12/1932 Wood.

10 J. SPENCER OVERHOLSER, Primary Examiner.

R. D. BALDWIN, Assistant Examiner. 

1. A METHOD OF CASTING MOLTEN METAL, WHICH METHOD COMPRISES TRANSFER OF HEAT FROM THE MOLTEN METAL TO EFFECT CHANGE OF STATE OF A BODY OF SECONDARY MATERIAL WHICH IS SUBJECT TO CHANGE OF STATE AT A TEMPERATURE LOWER THAN THE CONGEALING TEMPERATURE OF THE MOLTEN METAL BUT SUFFICIENTLY CLOSE TO SUCH TEMPERATURE SO THAT CHANGE OF STATE OCCURS COINCIDENTIALLY WITH THECONGEALING OF THE METAL BEING CAST, AND THEREBY USING LATENT HEAT OF THE SECONDARY MATERIAL TO ABSORB A PART OF THE HEAT OF THE MOLTEN METAL AND TO MAINTAIN APPROXIMATELY CONSTANT TEMPERATURE DIFFERENTIAL BETWEEN THE SECONDARY MATERIAL AND THE METAL BEING CAST THROUGHOUT A SUBSTANTIAL PART OF THE PERIOD REQUIRED FOR THE CONGEALING OF THE LATTER, WHEREBY SUCH CONGEALING PROCEEDS MORE RAPIDLY THAN ELSEWHERE. 